1. Technical Field
The present invention relates to a technique of driving an electrical load having a capacitive component.
2. Related Art
JP-A-7-130484 discloses a technique in which a plurality of capacitors connected in parallel are charged by using a power supply and the connection of the capacitors is switched from a parallel connection state to a series connection state as needed to generate a voltage higher than a voltage of the power supply, thereby driving an electrical load. By using the proposed technique, a voltage many times higher than a voltage generated by the power supply can be applied to the electrical load according to the number of capacitors connected in series.
A voltage waveform generated in this manner is a waveform whose voltage changes stepwise every time the number of capacitors connected in series increases or decreases. When a voltage generated by a capacitor is decreased and the number of capacitors is increased in proportion to the reduction in voltage, a highly accurate voltage waveform whose voltage change is small can be generated.
In the proposed technique, however, when it is intended to generate a highly accurate voltage waveform, there is a problem that the size of a circuit for generating a voltage waveform increases. For generating a highly accurate voltage waveform, it is necessary to generate a voltage waveform by decreasing a voltage generated by a capacitor and by using more capacitors. However, since a capacitor is relatively large, an increase in the number of capacitors increases the size of the circuit. Further for capacitors, a switch for connecting the capacitor to a power supply to charge the capacitor or a switch for connecting the capacitors in series is required. Therefore, when the number of capacitors increases, also the number of switches increases, resulting in a further increase in size of the circuit. Moreover, when the number of switches increases, the electrical resistance of the circuit increases, resulting in an increase in power loss or a reduction in response of the circuit. Therefore, it becomes impossible to follow a rapid change in voltage, which may make it hard to output a highly accurate voltage waveform.